On-board characterization of brake-wear emissions from a heavy-duty vehicle in real-world driving conditions

Abstract

Brake wear contributes significantly to non-exhaust emissions, with poorly documented real-world data on ultrafine particles and gaseous emissions, particularly for heavy vehicles. This study focuses on brake wear ultrafine particles emitted by a school bus in real-world driving conditions, through on-board measurements. Some gaseous compounds were also measured. Tests were conducted on a real-world school pick-up route, as well as an in-service-conformity compliant route. A custom-made stainless-steel emission collection system was designed and placed around the front right disc. Particle and gas measurement instruments were sampled directly from the collection system, which was also equipped with temperature sensors. Results show that brake particle emissions range from 4.1 × 10⁷ #/brake/km to 1.7 × 10⁹ #/brake/km, with a bimodal distribution (first mode around 10 nm and second mode around 200 nm). Emissions were analyzed with regard to energy loss during each braking event, showing it can be critical in estimating brake emissions in most cases. In some cases, particle emissions are poorly correlated with energy in the 10 nm mode, which is due to high-intensity and repeated braking episodes. Concentration peaks were also observed for a few volatile organic compounds such as benzene and toluene. Gaseous emission was also observed for CO, CO₂, CH₄, NH₃, NOx, and SO₂.

Glossary

Particle collection system, VOCs, high-intensity braking